Electrostiatic coating apparatus employing supersonic vibrations



De@ 17, 1963 sl-nzuo NlsHlYAMA ETAI. 3,114,654.

ELEcfrRosTATIc coATINc APPARATUS EMPLOYING suPERsoNIc VIBRATIoNs Filed Aug. 1e, 19Go 3 Sheets-Sheet 1 INVENTORS'. SH12 ua ,v/sH/ MMA SE1/ra funn Dec. 17, 1963 sHlzuo NISHIYAMA ETAL ELECTROSTATIC COATING APPARATUS EMPLOYING SUPERSONIC-VBRATIONS Filed Aug. 16, 1960 .3 Sheets-Sheet 2 De@ 17, 1953 I sHlzuo NlsHlYAMA ETAL 3,114,654

ELECTROSTATIC COATING APPARATUS EMPLOYING SUPERSONIC VIBRATIQNS Filed Aug. 16, 1960 5 Sheets-Sheet 3 fil-@ 10 5 /llllllllll///l l 17' /a// 7 20 SII/z uo Al nited States Patent Utilice Patented Dec. l?, i963 lFied Aug. 116, 19t/itl, Ser. No. @,026 Claims priority, application Iapnn Dec. 14, 1959 Claims. (Cl. 1l8-627) he present invention relates to a method of applying the coating material to a desired object, and more particularly to a method of coating, which is characterized in that the coating material is iinely pulverized and dispersed by means of super-sonic vibration and the coating material thus pulverized is adhered to a desired object by means of electrostatic force.

lt has heretofore been usual to use a coating device which utilizes corona discharge or compressed air for pulverizing the coating material.

in a so-called grid type electrostatic coating device, the coating material is injected from -a sprayer by compressed air and electrostatic field is acted on the pulverized coating material between the sprayer and the article to be coated so that the tine particles of coating material are caused to pass at a high speed and spread between the sprayer and the article to be coated by means of compressed air and it has disadvantage that the loss of coating material is large and it is diticult to obtain uniform coating.

The principal object of this invention is to obviate the above disadvantages by pulverizing the coating material with the aid of super-sonic vibration and without loss of the coating material and very uniformly and efficiently.

Another object of this invention is to provide a novel device for etfecting the method of this invention.

For a better understanding of this invention, reference is had to the accompanying drawings, in which:

FIG. l is a diagrammatic view of a device for carrying out the method of this invention.

FlG. 2 is a modified embodiment of the device.

NGS. 3, 4, 5 and 6` are diagram-matic views illustrating other modified forms of the device.

FIGS. 7, 8, 9 and 10 are partial sectional views illustrating various modi-ficatioins of the horn tip.

in all of these drawings, the same reference nurnerals designate the same or similar parts.

in an embodiment of this invention as shown in FlG. 1, l represents a super-sonic vibrator which lgenerally is provided with a nickel core 2 and coils (not shown) connected to a high frequency electric source d, thereby causing supersonic magneto striction vibration. 5 represents a horn having conical or gradually converging shape and it is rigidly secured to the super-sonic vibrator l at its base so that the top end 5 of the horn 5 is subjected to the concentration of the super-sonic energy when the vibrator l is driven electrically from the high frequency electric source `4.

6 represents a tank or reservoir for the coating material, which is connected to a pipe 7 through a regulating valve 8 and the end 7 of the pipe '7 is brought to open at a point adjacent to the tip 5' of the horn to discharge the coating material therefrom.

9 represents means for causing unidirectional electrostatic ield which consists, -as for instance, of a metal ring lll connected through a direct current high voltage source 1i to an article l2 to be coated.

The principle or" operation of this invention is characterized in that when the coating material in the tank 6 ows out of the tip end 7 of pipe 7 it contacts with the tip 5 of the horn 5 and subjected to a violent oscillation of the tip 5 and is pulverized ,and thrown in the direction of the arrows and the coating material thus pulverized is forced to adhere onto the article l2 to be coated by the electrostatic field applied between the ring l@ and the article l2. The speed of the particles of coating material iinely pulverized by the super-sonic vibration are very small and merely oat in the space so that coating material thus pulverized adheres to the article lf2 by the electrostatic orce without substantial loss.

In a modiiied form of the device according to this invention as shown in FIG. 2, the feed pipe 7 of the coating material is passed through the inside hole 7 of horn 5 and opens at its tip end 5. All the other parts are similar to those shown in FlG. l.

ln the embodiment of this yinvention as shown in FlG. 3, the horn 5 is so shaped that it has a long iiat tip 5 from which opposite sides gradually diverge to the rectangular base which is rigidly secured to a magneto striction core 2 and the lower end 7 of the pipe 7 is brought to make contact with one end of the t-ip portion 5. All the other parts are same as those shown in FIG. l.

By this arrangement, the area of the coating material making Contact with the mechanical vibrating body is increased so that the quantity of coating material to be sprayed is increased and also the iineness of sprayed particles of the coating material are very uniform.

In this embodiment, the symmetrically converged horn 5 for concentrating the super-sonic vibration is operated by the magneto striction vibrator l which is driven by the coil 2 connected to a high frequency electric source and has the at elongated tip end 5', the area of which is equal to tl 'and oscillate in the longitudinal direc-tion so that the coating material flowing out of the open end 7 of the feed pipe makes contact with the oscillating surface 5 of the horn 5 and then subjected to a violent oscillation of the surface 5 and advances upwards as shown by the arrows B and it is dispersed as a thin film on the vibrating surface 5 and then it is discharged into the space as line particles. The `finely pulverized particles of the coating material thus issued are guided to the article 12 to be coated thereon by means or unidirectional electrostatic lield applied between the object and tip 5' of the horn 5'. The phenomena of coating material advancing upwards along the tip surface 5' and then pulverized and thrown out has been practically proved for the irst time by the inventors and by this phenomena the Contact area of the coating material with oscillating surfa 5 is increased so that the quantity of coating material to be sprayed lis increased and the coating material, after dispersed on the vibrating surface 5 as a thin film, is pulverized. By this means the particles of the coating mate rial can be more finely pulverized and has characteristic of that the fineness of particles thus pulverized remains uniform during the continuous operation for a long time.

in the embodiment as shown in FIG. 4, a piece i3 having a special shape, for instance, a semi-spherical shape is attached to the tip o'f the horn 5 and the feeding hole 7 provided through the horn is communicated with two or more small holes lili provided in the piece 13. All the remaining parts are same as those shown in FIG. l. In this embodiment the semi-spherical piece i3 secured to the tip end of horn 5 is violently oscillated by means of the magneto striction vibrator il and the coating material flowing out of the small holes M- is formed into a thin film over the surface of the piece i3 and ejected in the direction of the arrows C, and pulverized, and then adhered to the article l2 by means of DC. electrostatic force so that the line particles of coating material do not concentrate only in the central axial direction D but also sprayed into the space for a wide range. The small holes 5.4 may be provided for a desired number in order to further increase the effect of dispersion. Moreover the shape of the top piece i3 may be changed, for instance,

to an ellipsoid or any other shape suitable for dispersing the spray.

In the embodiment as shown in FIG. 5, a tip portion 5c of the conical horn 5 `for concentrating super-sonic vibration is made of a conducting material and the remaining part of the horn is made of insulating material. All the other arrangements are same as those shown in FIG. 2 except the conducting tip of the horn which is connected to a high voltage source of direct current. In this arrangement, the operation is same as that already described and the horn 5 of insulating material has advantage of avoiding the stray field and proving insulation between the supersonic vibrator and the direct current hi gh voltage source.

In the embodiment as shown in FIG. 6, the units as shown in FIGS. 1 or 2 is assembled in parallel and the tip 5', 5 of the horn 51 and 52 surounded by a metal ring I@ which is connected to a direct current high voltage source (not shown).

By this arrangement the pulverized coating material issuing from the tips of the horns extends in vertical rows like an elliptic form. Thus by assembling a desired number of the horns and super-sonic vibrating units the range or length of the coating area can be increased or elongated as desired.

According to this invention, the fine particles of coating material can be sprayed and dispersed in a desired direction and also the iineness of the sprayed particle can be made smaller and more uniform by changing the shape of the tip of horn. Some examples of which are shown in FIGS. 7, 8, 9 and 10.

In FIG. 7, a small knob 15 is attached to or made integral of the tip of the horn 5 to form a cup-shaped space communicating with the feed hole of the coating material. In this construction the coating material delivered to the cup-shaped space 16 is pulverized by super-sonic vibration of the horn 5 and sprayed out along the axis of the horn.

In FIG. S, a disc 17 having almost same diameter as the tip of the horn 5 is secured to or made integral thereof to form a circular gap between them. In this case the coating material is dispersed almost radially.

Ir the disc 17 in FIG. 8 is made smaller in diameter than that of the tip of the horn as shown by 17 in FIG. 9, then the coating material is ejected along the direction shown by the arrow extending about 45 to the axis of the horn.

If the knob 19 as shown in FIG. 10 is secured to the tip of the horn to form a semi-circular groove between them the coating material can be sprayed in a direction almost similar to that of FIG. 9. In the embodiments shown in FIGS. 7 to 10, the coating material supplied through the hole 7 provided in the horn is filled in the small gap around the tip by capillary action and is pulverizcd very finely by the supersonic vibration by designing the gap very narrow so that the coating material can be adhered to the article uniformly. Moreover, since the thickness of the gap is very thin and the particle therein is also very thin the static torce corresponding thereto is only the molecular attraction due to the capillary action and the effect of gravity may be substantially neglected. Since the dispersion of the coating material is caused by super-sonic vibration along the thin gap irrespective of the direction of the horn the most efficient coating can be elected by considering the condition of position of the device in case of coating. If the gap is too large a fibrous insert such as a felt washer may be inserted in the gap to obtain the similar result to a thin gap.

What we claim is:

1. A device for applying coating material to an article comprising a magneto striction source for generating supersonic vibrations, a converging horn, the base of which is rigidly secured to said source for transmission of th vibrations from said source and concentrating said vibrations to the tip of said horn, said tip comprising a semispherical tip having a plurality of small holes communieating between a central hole in said horn and thc surface of said tip, means for feeding the coating material through the holes in said tip to the surface thereof thereby to eject said material in a spray towards said article and means for establishing a direct current electrostatic held between said spray of said material and said article.

2. A device for applying coating material to an article comprising a magneto striction source for generating supersonic vibrations, a converging horn, the base ot which is rigidly secured to said source for transmission ci the vibrations from said source and concentrating said vibrations to the tip of said horn, said tip being formed with a cup-shaped gap, means for feeding said material into said gap, thereby to eject said material in a spray towards said article and means for establishing a direct current electrostatic field between said spray ot' said material and said article.

3. A device for applying coating material to an article comprising a maaneto striction source for generating supersonic vibrations, a converging horn, the base of which is rigidly secured to said source for transmission or the vibrations from said source and concentrating said vibrations to the tip of said horn, said tip being formed with a thin circumferential gap which is substantially the same diameter as the tip, means for feeding material into said gap, thereby to eject said material in a spray towards said article and means for establishing a direct current electrostatic field between said spray of said material and said article.

4. A device for applying coating material to an article comprising a magneto striction source for generating supersonic vibrations, a converging horn, the base of which is rigidly secured to said source for transmission of the vibrations from said source and concentrating said vibrations to the tip of said horn, said tip being formed with a thin circumferential gap which is smaller than the diameter of said tip, means for feeding material into said gap thereby to eject said material in a direction of 45 with respect to the axis of the horn in a spray towards said article and means vfor establishing a direct current electrostatic eld between said spray of said material and said article.

5. A device for applying coating material to an article comprising a magneto striction source for generating supersonic vibrations, a converging horn, the base of which is rigidly secured to said source for transmission of the vibrations from said source and concentrating said vibrations to the tip of said horn, said tip being formed with semicircular grooves formed therein, means for feeding the coating material into said grooves thereby to eject said material in a direction `diverging about the axis of the horn in a spray towards said article and means for establishing a direct current electrostatic field between said spray of said material and said article.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A DEVICE FOR APPLYING COATING MATERIAL TO AN ARTICLE COMPRISING A MAGNETO STRICTION SOURCE FOR GENERATING SUPERSONIC VIBRATIONS, A CONVERGING HORA, THE BASE OF WHICH IS RIGIDLY SECURED TO SAID SOURCE FOR TRANSMISSION OF THE VIBRATIONS FROM SAID SOURCE AND CONCENTRATING SAID VIBRATIONS TO THE TIP OF SAID HORN, SAID TIP COMPRISING A SEMISPHERICAL TIP HAVING A PLURALITY OF SMALL HOLES COMMUNICATING BETWEEN A CENTRAL HOLE IN SAID HORN AND THE SURFACE OF SAID TIP, MEANS FOR FEEDING THE COATING MATERIAL THROUGH THE HOLES IN SAID TIP TO THE SURFACE THEREOF THEREBY TO EJECT SAID MATERIAL IN A SPRAY TOWARDSSAID ARTICLE AND MEANS FOR ESTABLISHING A DIRECT CURRENT ELECTROSTATIC FIELD BETWEEN SAID SPRAY OF SAID MATERIAL AND SAID ARTICLE. 